Chain shortened polypeptide repeat n c s nh c o ch r

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chain shortened polypeptide + repeat N C S = NH C O = CH-R a phenyl thiohydantoin
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A Mechanism for the Cyclization and Cleavage NHCHC-NHCHC O = O = R R' NHC S = H 3 O + NHC :S: = N : H CH R C O = NHCHC R' O = The above bonding changes are promoted by acid-catalysis. hydrolysis of thioester H 3 O + H 2 O NHC S = NH CHR C O = HO (-H 2 O) N C S = NH C O = CH-R a phenyl thiohydantoin NHC S N = C CH R O + H 3 NCHC + O = R' chain-shortened polypeptide unstable
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The phenylthiohydantoin is compared with a family of such compounds prepared from the standard amino acids to identify the N-terminal amino acid . The polypeptide that remains is further degraded by the Edman method to identify the next N-terminal amino acid. When automated, about 60 amino acid residues can be "sequenced" before side products begin to interfere. The first "protein sequenator" was demonstrated by Edman in 1967. Automated Amino Acid Sequencer C-Terminal Residues Enzymatic hydrolysis with digestive enzymes called carboxypeptidases specifically hydrolyze the amide bond of the amino acid residue with the free carboxyl group. The enzyme will continue to hydrolyze off the C-terminal amino acid groups. To determine the original C-terminal amino acid of a polypeptide, the analysis must be carried out as a function of time. The first appearing free amino acid is the original C-terminal residue.
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